Bromobutyl rubber-styrene-acrylonitrile graft copolymers

ABSTRACT

Novel high impact plastics are prepared by the inclusion of 2 to 30 weight percent of bromobutyl rubber in polymers of styrene and styrene-acrylonitrile and the grafting of said polymers onto said rubber. The graft copolymers are obtained by polymerizing the monomers of styrene or styrene-acrylonitrile in the presence of the bromobutyl rubber, which is preferably precrosslinked.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of Ser. No. 497,688 entitled "Chlorobutyl Rubber-Styrene-Acrylonitrile Graft Copolymers" filed on Aug. 15, 1974 now U.S. Pat. No. 3,954,911, said parent application being hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to plastic composite materials, which are polymers having grafted thereon rubbery polymers. The matrix phase polymer, such as polystyrene, is produced in the presence of the included rubbery phase polymer thus during this highly excited state the polystyrene is grafted onto the rubbery polymer.

The plastic composite materials have gained wide market acceptance as low cost engineering plastics. These materials exhibit exceptional impact strengths. The plastic composite materials generally are prepared by dissolving a rubber such as polybutadiene or SBR in the polymerization monomer, such as styrene. This mixture is then polymerized by means of thermal or free radical initiation to an intermediate degree of monomer polymerization, e.g., 20-30% conversion. The prepolymer thereby produced is then suspended in an aqueous medium and the polymerization continued to completion in suspension. The resultant graft composite is recovered, washed dried and extruded.

Although these composite materials are widely used, they have exhibited inferior stability to outdoor aging. Various techniques have been tried to improve stability, such as compounding with conventional stabilizers or attempting to select an improved combination of composite materials. In this latter regard, EPR has been substituted for SBR and polybutadiene as the rubber component. It is an advantage of the present invention that a graft copolymer of a thermoplastic material and rubber possessing improved stability has been discovered. It is a particular feature of the present invention that a single continuous copolymerization process has been devised. It is a particular advantage of the present invention that suitable graft copolymers can be produced by several variations of the general process for producing graft copolymers. It is a particular feature of the present invention that the graft copolymers produced have superior weather resistance. A particular feature of the present invention is the omission of a bulk polymerization in one embodiment thereof. These and other advantages and features will become apparent from the following discussion of the invention.

DRAWINGS

The FIGURE is a graph of comparative test data for chlorobutyl rubber.

SUMMARY OF THE INVENTION

Briefly stated, the present invention is a novel graft copolymer of a thermoplastic matrix of polystyrene or a copolymer of styrene and acrylonitrile and an included phase of bromobutyl rubber. The present invention also lies in the process of producing the novel graft copolymers. A particular embodiment of this is a method for producing the graft copolymers which comprises imbibing styrene or styrene-acrylonitrile monomer in crosslinked bromobutyl rubber, dispersing said imbibed rubber in an aqueous suspension, said rubber comprising 2-30 weight percent based on the total amount of styrene or styrene-acrylonitrile monomer present in the said suspension, polymerizing said styrene or styrene-acrylonitrile and recovering a graft copolymer of styrene or styrene-acrylonitrile and crosslinked bromobutyl rubber.

DETAILED DESCRIPTION OF THE INVENTION

In the present novel graft copolymers, the backbone of the polymer, i.e., the matrix phase, is comprised of polystyrene or a copolymer of styrene and acrylonitrile. The rubbery phase which is included or grafted onto the backbone is bromobutyl rubber.

In the parent application, a polymerization process was detailed based on the use of chlorobutyl rubber.

Butyl rubber per se is an unacceptable material for impact polystyrene production for (at least) two reasons, i.e., (1) it has a relatively low concentration of allylic hydrogens for the grafting reaction, and (2) it does not crosslink in the free radical environment of the styrene polymerization.

It was shown in the parent application that chlorobutyl rubber was an ideal material for such polymerization. It resulted in a process whereby:

(1) Much increased grafting was obtained via allylic chlorines which have increased free radical chain transfer activity relative to allylic hydrogens;

(2) The elastomer was precrosslinked by a technique which did not hamper the subsequent styrene polymerization (i.e., thermal treatment); and

(3) The microgel particle size was set by a high shear blending operation on swollen macrogel particles.

It has recently been considered whether bromobutyl rubber would be a suitable equivalent for the process described in Ser. No. 497,688 for chlorobutyl.

A literature study has uncovered a comprehensive article.sup.(1) showing that bromobutyl has essentially the same allylic halide configurations as its analog, chlorobutyl rubber. The carbon-bromine bond is known to be weaker.sup.(2) than the corresponding carbon-chlorine bond and therefore more prone to chain transfer. Thus, it would be expected that the use of bromobutyl rubber in the process of Ser. No. 497,688 in place of chlorobutyl would result in at least equivalent grating efficiency and probably superior.

Bromobutyl can be precrosslinked as readily and perhaps more readily with at least the same crosslinking agents as will crosslink chlorobutyl. It is likely that bromobutyl will result in a higher crosslink density than chlorobutyl with a wider range of crosslinking techniques.

The particle size of a bromobutyl precrosslinked, swollen rubber would be analogous to the described chlorobutyl case.

Bromobutyl rubber is a brominated butyl rubber. Butyl rubber is a copolymer of small amounts, less than 30% and preferably about 1 to 3%, of isoprene and a major proportion of isobutylene. The butyl rubber is produced by reacting the isoprene and isobutylene at low temperatures, -80 to -165 degrees C., in a slurry in an alkyl halide, such as methyl chloride, preferably with a Friedel-Crafts catalyst such as AlCl₃. This slurry passes to a flash drum where it is contacted with a hot solvent, e.g., hexane at 0 to 100 degrees C., which solubilizes the rubber and drives off the alkyl halide. The product rubber is then brominated by introducing a stream of bromine into the hot solvent containing the butyl rubber.

The halogenation is carried out such that the rubber contains about 0.5 weight percent bromine but not more than 1.0 "X" weight percent bromine wherein: ##EQU1## L= mol percent of isoprene in the polymer. This limitation stated otherwise is to the effect that the rubber should not have a bromine content exceeding about 1 atom of bromine per double bond of the rubber. Details on the preparation of bromobutyl rubber are readily available to those of skill in the art, for example, U.S. Pat. No. 2,631,984.

Novel graft copolymers according to the present inventions are obtained by commingling the bromobutyl rubber in the styrene monomer or mixture of styrene monomer and acrylonitrile monomer, which is then polymerized. Only a minor amount, i.e. about 2 to 30 weight percent of the rubber based on polymerizable monomer is added to the monomer to obtain the benefits of the present invention. Preferably about 5 to 8% rubber is dissolved in the monomer prior to polymerization. In addition to the polymerizable monomer, inert solvents for the rubber and resultant graft copolymer may be present such as C₅ to C₁₀ saturated by hydrocarbons, i.e., the conventional rubber solvents, e.g., n-hexane.

When styrene-acrylonitrile polymers are being produced, the polymerizable monomers are generally present in the polymerization in the range of 20 to 90 weight percent styrene and 10 to 80 percent acrylonitrile, preferably about 50 to 80 percent of the polymerizable monomer is styrene. The resulting polymer will contain relative weight percents of monomer constituents in the substantially same ratio as the polymerization.

The process of polymerization of the monomer is carried out under conditions which will abstract the allylic bromine atoms in the rubber to achieve grafting. This condition is achieved with free radical initiators, such as organic peroxides or hydroperoxides, e.g., benzoyl peroxide, azo or diazo compounds and other well known methods, such as UV or ionizing radiation. The reaction may be carried on in the solvent, however, an emulsion polymerization in an aqueous phase is more conveniently conducted after the formation of a prepolymer (i.e., at about 20-30 conversion of the polymerizable monomer). Although the process is conducted under conditions designed to abstract allylic bromine, this is only a proposed mechanism and it is not intented to limit the scope of the invention.

The bulk polymerization can be carried out at temperatures in the range of 0 to 250 degrees C., preferably 50-150 degrees C. generally at 1 to 50 atmospheres, although subatmosphere pressure or autogenous pressure can be used. Usually an inert atmosphere such as nitrogen will be used.

A suitable process for preparing the present graft copolymers employs a bulk polymerization of a solution of the bromobutyl rubber in the polymerizable monomer with or without inert solvents. The reaction is carried out as noted above to about 20 to 30% conversion with continuous stirring, at which time the reaction is stopped and the prepolymer dispersed in an aqueous suspension along with the other components from the bulk reaction (i.e., unreacted polymerizable monomer and inert solvent). After about 15% conversion, the polystyrene in styrene solution, e.g., becomes the favored phase and an inversion occurs. A further discussion of inversions of this type may be found in an article by H. Keskkula et al appearing in J. Ap. Poly. Sci., 15, 351 (1971). Well known bulk polymerization techniques were employed for this procedure as shown in the prior art by G. F. Freeguard and M. Karmarkar, J. Ap. Poly. Sci., 15, 1649 (1971); 16, 69 (1972).

It has been found that the suspension polymerization is carried out most successfully if the predominately rubber phase is dispersed generally to a particle size of 10 microns or less. The suspension polymerization is generally carried out at 50-150 degrees C. or preferably 70-110 degrees C.

In a particular aspect of the present invention, it has been found that the prepolymer preparation can be omitted and the polymerization can be begun and completed in suspension. This unexpected improvement can be achieved by crosslinking the bromobutyl rubber prior to copolymerizing the polymerizable monomer therewith. The bromobutyl rubber is conveniently crosslinked by heating a solution of dissolved rubber at a temperature of 100-160 degrees C. until an insoluble, crosslinked material is produced. Suitable solvents include hydrocarbons, such as the C₅ -C₁₀ hydrocarbons, both reactive and inert, such as styrene, hexane, pentane, ethylbenzene, xylene and the like. Generally only the amount of solvent necessary to dissolve the rubber will be employed. The crosslinked bromobutyl rubber is substantially insoluble in these solvents, however it will imbibe both polymerizable monomers and inert solvents. Alternately crosslinked bromobutyl rubber can be prepared by heating the solid rubber at temperatures of 100-200 degrees C. for sufficient time, e.g., up to 24 hours to crosslink the material.

The degree of crosslinking obtained by crosslinking the dissolved bromobutyl rubber is probably somewhat less than that obtained by crosslinking the solid rubber. When the solvent employed to dissolve the bromobutyl rubber is a reactant, i.e., styrene, the resultant crosslinked rubber also contains grafted polystyrene. Generally these "master batches" are prepared in a manner similar to the bulk polymerization, but without stirring and for longer times, e.g. up to 90 hours, and only small amounts of the polymerizable monomer, styrene or acrylonitrile, are present, i.e. sufficient to dissolve the bromobutyl rubber.

In a preferred process embodiment, crosslinked bromobutyl rubber is obtained by a homogeneous thermally induced curing of bromobutyl rubber, preferably in the absence of any solvent.

The crosslinked bromobutyl rubber (or bromobutyl rubber-styrene-acrylonitrile master batch) is substantially insoluble in solvents of the polymerizable monomers. The solvents and monomers are, however, imbibed by the crosslinked rubber (or master batch) causing it to swell to a gel-like mass. The total amount of polymerizable monomer (styrene and styrene-acrylonitrile) is adjusted to provide a bromobutyl rubber concentration in the range of 2 to 30 weight percent in the final polymerization. The gel is dispersed by any conventional means, such as whipping, grinding, crushing, or the like, provided that a predominate amount of the crosslinked rubber is dispersed to particles of less than 10 microns in size, preferably essentially all of the crosslinked rubber (or master batch) is less than 10 micron size.

The prepolymer from the bulk polymerization, the crosslinked bromobutyl rubber or master batch of crosslinked bromobutyl rubber and styrene or styrene-acrylonitrile are polymerized after dispersing the gel in substantially the same manner, i.e., the gel is dispersed to less than 10 micron size and a free radical suspension polymerization carried to completion. The same free radical catalyst may be employed and other conditions and reaction times are substantially the same. The recovered polymers are similar graft copolymers according to the present invention, with the principal difference being the degree of crosslinking of the bromobutyl rubber. The degree of crosslinking based on the material dispersed in the suspension is crosslinked bromobutyl rubber> master batch bromobutyl rubber-styrene or styrene acrylonitrile> prepolymer.

The graft copolymers of the present invention can be characterized as comprising a matrix phase of essentially non-grafted polymer, polystyrene or styrene-acrylonitrile copolymer. Contained in this matrix is a bromobutyl rubber included phase to which is grafted some matrix phase polymer. The bromobutyl rubber included phase also contains a substantial proportion of included but non-grafted matrix phase polymer. Generally the total fraction of occluded but non-grafted matrix phase polymer in the F.rubber phase is considerably greater than the fraction of matrix phase polymer grafted to the bromobutyl rubber.

Bromobutyl rubber shows a relatively high transfer activity in the polymerization of monomer with included bromobutyl rubber and only moderate retardation of the polymerization rate. The high chain transfer constant of bromobutyl rubber and the difficulty in separating homopolymer from the copolymer product demonstrates that grafting has occurred.

The following examples carried out with chlorobutyl rubber illustrate the present invention and in particular describe the many various possible permutations thereof, since bromobutyl is an equivalent for chlorobutyl. Although there are numerous detailed examples, they are only illustrative and do not entirely span the scope of the invention herein disclosed. In the examples, percents are by weight unless otherwise specified.

Although not recited in the data, particle size of the elastomer phase was frequently determined and is the basis for the range of particle size recited hereinabove. Particle size of the elastomer phase was estimated by pressing a single bead between two glass slides at 200 degrees C. and viewing with a Spencer AO light microscope at 537X magnification. In cases where elastomer phase particles could not be seen, they were assumed to be less than 5μ in diameter.

EXAMPLES 1-15

The graft copolymers of the present invention have been prepared by several methods. In these examples, chlorobutyl rubber (as described in Ser. No. 497,688) was dissolved in a polymerizable monomer and the bulk polymerization carried out to the desired point at which time the prepolymer reaction mixture was suspended in an aqueous system and the reaction continued to completion using the following procedure: All weights in 100 parts by weight styrene:

1. After bulk polymerization: Add 3 parts styrene containing 0.005 parts lecithin, 0.02 parts Bisphenol A, and 138 parts of suspension system containing water and 0.3 parts GH-20 (high molecular weight polyvinyl alcohol), 0.08 parts KH-17 (low molecular weight polyvinyl alcohol), 2.8 parts Na acetate.

2. Heat additional 2 or 3 hours at 90 degrees C., stirring at 300-350 rpm.

3. Add 0.15 parts benzoyl peroxide (wash in with water). Raise temperature to 95-100 degrees C.

4. add additional 0.15 parts benzoyl peroxide if beads do not appear to be hardening.

5. Usually leave stirring overnight at 90 degrees C.

6. filter, wash and dry.

The conditions of the bulk polymerizations, reactants, temperatures, manipulations are given in Table I below. The results from the physical testing are given in Table II. Injection molded samples for mechanical property evaluations were prepared from the beads on a Frohring Minijector using a barrel temperature of about 400 degrees F. for polystyrenes and about 500 degrees F. for ABS-type composites. The mold was maintained at room temperature. Samples were held two days or longer at room temperature prior to testing. Flexural Modulus was ASTM D-790, Procedure A; Tensile, yield and % Elongation, Fail were ASTM D-638 (cross-head speed= 2 inches per min.), Izod Impact was ASTM D-256, Method C; Melt Flow (MF) was ASTM D-1238, Condition L or P.

                                      TABLE I                                      __________________________________________________________________________     BULK POLYMERIZATION                                                            __________________________________________________________________________              Acrylo-                                                                    Styrene                                                                            nitrile                                                                            HT 1066(1)             Time,                                                                              Temp                                   Example                                                                             gms gms.                                                                               gms.         Other     hrs.                                                                               (deg. C.)                              __________________________________________________________________________     1    270 None                                                                               26     (0.2 ml DoSH, 0.25 gms Bz.sub.2 O.sub.2                                                        51/2                                                                               90                                                         + 0.25 gms at T.sub.o + 41/2 hrs.)                         2    270 "   26     0.25 gms Bz.sub.2 O.sub.2                                                                      41/2                                                                               90                                     3.sup.6                                                                             263 "   26     None            71/2                                                                               122                                    4    350 "   39     0.3 ml DoSH     15  122                                    5    486 "   39     (0.25 ml DoSH, 0.25 gms Bz.sub.2 O.sub.2)                                                      13  90                                                         (100 ml n-heptane                                                                              (12)                                                                               (90)                                   6    486 "   39     (0.25 ml DoSH, 0.25 gms Bz.sub.2 O.sub.2                                                       (10)                                                                               (80)                                                       20 ml MEK)                                                 7.sup.2                                                                             239 "   39     75 gms HPS/174 gms Styrene                                                                     8   122                                    8    486 "   39     35 ml MEK       16  110                                    9    370 108 39     None            61/2                                                                               100                                    10   370 108 39     100 ml n-heptane                                                                               6   100                                    11   370 108 78     None            111/2                                                                              100                                    12.sup.2,5                                                                          370 108 39     100 ml n-heptane, 0.3 gms                                                                      11  60                                                         Bz.sub.2 O.sub.2                                           13.sup.3,7                                                                          370 108 85.3   100 ml n-heptane                                                                               8   100                                    14.sup.3,4,8                                                                        370 108 39     100 ml benzene  6   100                                    15.sup.3,4,8                                                                        370 108 39     100 ml benzene  6   100                                    __________________________________________________________________________      Abbreviations:                                                                 HPS = Homopoly styrene                                                         DoSH = n-dodecyl mercaptan                                                     Bz.sub.2 O.sub.2 = Benzoyl peroxide                                            MEK = methyl ethyl ketone                                                      .sup.1 Chlorobutyl rubber unsaturation 1.1 to 1.7% chlorine content 1.1 t      1.3%, Exxon Chemical Co., U.S.A.                                               .sup.2 Particle size adjusted prior to suspension polymerization by Warin      blender mixing for 3 minutes                                                   .sup.3 Particle size adjusted prior to suspension polymerization by Warin      blender mixing for 5 minutes                                                   .sup.4 1% calcium stearate for stability                                       .sup.5 2% calcium stearate for stability                                       .sup.6 Plasticord 5 min. at 170 deg. C. 50 RPM after suspension                polymerization                                                                 .sup.7 23 hours drying in 150 deg. C. oven after suspension polymerizatio      .sup.8 24 hours drying in 150 deg. C. oven after suspension polymerizatio

                                      TABLE II                                     __________________________________________________________________________     RESULTS OF TESTING                                                             __________________________________________________________________________                                               Notched Izods                        Chlorobutyl               Tensile  Flex   (ft lbs/in. Notch)                        rubber               Yield                                                                              % Elong.                                                                            Mod. × 10.sup.-.sup.3                                                           Room                                 Example                                                                             wt.%  MF.sub.230 (2.16 Kg)                                                                   MF.sub.190 (5 Kg)                                                                     (psi)                                                                              fail (psi)  Temp.                                                                              -20 deg. F                       __________________________________________________________________________     1    8.8   9.6            5980                                                                               --   375    0.64                                                                               2.8**                            2    8.8   6.9            5620                                                                               --   370    0.64                                                                               --                               3    9.0   0.49           7218                                                                               --   370    0.65                                                                               3.4**                            4    10.0  0.96           6520                                                                               --   343    0.72                                                                               4.8**                            5    7.4   7.1            6630                                                                               10.9 342    0.57                                                                               3.5**                            6    7.4   2.3            8230                                                                               6.5  352    0.66                                                                               3.9**                            7    7.4   4.7            6380                                                                               5.2  373    0.42                                                                               0.28                             8    7.4   0.79           6940                                                                               5.0  367    0.42                                                                               0.26                             9    7.5   0.16           --  --   371    0.62                                                                               --                               10   7.5   1.1            --  --   370    1.68                                                                               1.30                             11   14.0  --             3709                                                                               4.7  278    0.74                                                                               0.71                             12   7.5   --             5603                                                                               4.9  329    0.58                                                                               0.53                             13   15.1  --             --  --   283    0.60                                                                               1.44                             14   7.5   --             --  --   351    0.74                                                                               0.55                             15   7.5   --             --  --   304    0.70                                                                               0.58                             __________________________________________________________________________      **Unnotched                                                              

EXAMPLES 16-22

In these examples, there was no bulk polymerization as such, however, product graft copolymer master batches were prepared as described below in TABLE V, chopped, imbibed, dispersed, etc. as indicated below in TABLE III, then subjected to suspension polymerization. The same test procedures as described above were employed and the results are set out below in TABLE IV.

                  TABLE III                                                        ______________________________________                                                                   Particle Size                                                                  Adjustment                                           Example  Other*           Via                                                  ______________________________________                                         16       130 gms. chopped Waring blend mix                                              copolymer A      5 min.                                               17       260 grams chopped                                                                               Waring blend mix                                              A                5 min.                                               18       130 gms. chopped B                                                                              Waring blend mix                                                               5 min.                                               19.sup.2,3                                                                              130 grams chopped C                                                                             Waring blend mix                                              100 ml n - heptane                                                                              5 min.                                               20.sup.3 130 gms chopped D                                                                               Waring blend mix                                              100 ml n - heptane                                                                              5 min.                                               21.sup.1,5                                                                              65 gms chopped E Waring blend mix                                              75 gms HPS/146 gm                                                                               3 min.                                                        styrene                                                               22.sup.4 130 gms chopped E                                                              80 ml MEK        None                                                 ______________________________________                                          *A - E defined in TABLE V                                                      .sup.1 19.5 grams HT 1066                                                      .sup.2 Extruded at 400 deg. F.                                                 .sup.3 0.5% calcium stearate for stabilizing                                   .sup.4 0.3% calcium stearate for stabilizing                                   .sup.5 18 hours drying in 150 deg. C. oven after suspension polymerizatio

                  TABLE IV                                                         ______________________________________                                         RESULTS                                                                        ______________________________________                                                                        Notched Izods                                   Tensile             Flex       (ft lbs/in.Notch)                                      Yield   % Elong. Mod. × 10.sup.-.sup.3                                                             Room                                          Example                                                                               (psi)   fail     (psi)    Temp. -20 Deg. F.                             ______________________________________                                         16     7764    7.3      344      0.69  0.31                                    17.sup.1                                                                              6646    8.0      320      0.95  0.77                                    18.sup.2,3                                                                            7034    7.8      338      1.06  0.50                                    19     1724    21.7     308      0.61  0.48                                    20     1503    17.7     297      0.85  0.63                                    21     9523    6.3      366      0.88  0.82                                    22     7723    7.6      337      0.49  0.57                                    ______________________________________                                          .sup.1 Later repeat gave RTN Izod of 1.40                                      .sup.2 Later repeat gave RTN Izod of 1.22, -20 deg. F., - 0.57                 .sup.3 MF.sub.230 (2.16Kg) = 0.33                                        

TABLE V

A master batch was prepared by dissolving chlorobutyl rubber in styrene monomer in a 2 liter resin kettle under nitrogen, then placing portions in unstirred bottles in an oven under 4 psig of nitrogen according to formula below.

                  TABLE V                                                          ______________________________________                                                           Heating Schedule                                                    Styrene   HT 1066,   Time,   Temp.                                      RUN    gms       gms        hrs     (Deg. C.)                                  ______________________________________                                         A      461       183        48      100                                                                    781/2   125                                        B      461       183        48      100                                                                    72      120                                                                    24      150                                        C      461       183        641/2   100                                                                    48      120                                        D.sup.1                                                                               --        --         24      150                                        E.sup.2                                                                               490       183        24      60                                                                     651/2   80                                         ______________________________________                                          .sup.1 Same as C but continued for additional period of time                   .sup.2 1.0 gram benzol peroxide added                                    

EXAMPLES 23-31

In examples 23-31, precrosslinked chlorobutyl rubber is imbibed and then either subjected to bulk polymerization as described above for Examples 1-15 or subjected directly to solution polymerization. The same procedures as described above were employed in the polymerization and preparative process is set out in TABLE VI and the test results are in TABLE VII. The precrosslinked chlorobutyl rubber was obtained by heating pieces of HT 1066 (1 cc or less in average volume) in a vacuum oven at 20 mm Hg, 150° C. for 24 hours (Example 24--18 hours). The crosslinked rubber was imbibed with styrene or other materials as indicated in TABLE VI.

                                      TABLE VI                                     __________________________________________________________________________     BULK POLYMERIZATION                                                            __________________________________________________________________________              Acrylo-                                                                            X-L                     Particle Size                                  Styrene,                                                                           nitrile,                                                                           Rubber,       Time,                                                                              Temp. Adjustment                                Example                                                                             gms gms gms  Other    hrs Deg. C.                                                                              Via                                       __________________________________________________________________________     23.sup.1                                                                            370 108 39   100 ml n-heptane                                                                        83/4                                                                               100   Waring blend 1 min.                       24.sup.1                                                                            486 None                                                                               39   None     None                                                                               None  Waring blend mix 5 min.                   25.sup.1                                                                            370 108 39   100 ml n-heptane                                                                        2   100   Waring blend mix 5 min.                   26.sup.2                                                                            370 108 56   100 ml n-heptane                                                                        21/2                                                                               100   Waring blend mix 5 min.                   27.sup.3                                                                            370 83  39   100 ml n-heptane                                                                        71/2                                                                               100   Waring blend mix 5 min.                   28.sup.3                                                                            486 None                                                                               39   100 ml n-heptane                                                                        None                                                                               None  as in 31                                  29.sup.4                                                                            515 None                                                                               41.2 None     None                                                                               None  Waring blend 1 min.                                                            Gear pump 20 min.                         30.sup.4                                                                            515 None                                                                               41.2 None     None                                                                               None  Waring blend 1 min.                                                            Gear pump 35 min.                         31.sup.5                                                                            486 None                                                                               39   None     None                                                                               None  Waring blend 1 min.                                                            Silverson mix 5 min.                                                           rough shear, 5 min.                                                            med, shear, 5 min.                                                             high shear.                               __________________________________________________________________________      .sup.1 0.1% Calcium stearate for stabilization, 24 hours drying of produc      in 150 deg. C. oven                                                            .sup.2 0.3% Ionol 0.3% 2,2"  - methylene - bis (4-methyl-6-t-butyl phenol      0.5% calcium stearate for stabilization.                                       .sup.3 0.5% Ionol, 0.5% 2,2" - methylene - bis (4-methyl-6-t-butyl phenol      0.1% calcium stearate for stabilization                                        .sup.4 0.25% calcium stearate                                                  .sup.5 1.5 × suspension formula given in Example 1 - 15            

                                      TABLE VII                                    __________________________________________________________________________     TEST RESULTS                                                                   __________________________________________________________________________                                 Notched Izods                                                  Tensile  Flex   (ft. lbs/in.Notch)                                             Yield                                                                              % Elong.                                                                            Mod. × 10.sup.-.sup.3                                                           Room                                               Example                                                                             MF.sub.190 (5 Kg)                                                                     (psi)                                                                              fail (psi)  Temp.                                                                              -20 Deg.F.                                     __________________________________________________________________________     23   --     --  --   347    0.53                                                                               0.57                                           24   --     --  --   320    1.31                                                                               0.57                                           25          --  --   307    0.90                                                                               0.54                                           26   0.08   --  --   312    0.98                                                                               0.56                                           27   0.10   3392                                                                               7.3  264    0.95                                                                               0.41                                           28.sup.1                                                                            3.4    2606                                                                               31.3 180    2.39                                                                               0.37                                           29   0.36   6870                                                                               6.7  341    0.77                                                                               0.55                                           30   0.56   5372                                                                               5.9  284    1.53                                                                               0.70                                           31   0.62   5813                                                                               11.5 306    0.95                                                                               0.57                                           __________________________________________________________________________      .sup.1 Bubbles in impact/stiffness specimens                             

EXAMPLES 32-34

Examples 32-34 were carried out as Examples 1-15, that is, without crosslinked or prereacted rubber and without a bulk polymerization. The suspension polymerization formulation of Examples 1-15 was employed. The reaction procedure is set out in TABLE VIII and the results in TABLE IX.

                  TABLE VIII                                                       ______________________________________                                                          Chlorobutyl                                                           Styrene  Rubber                                                        Example gms      gms        Other                                              ______________________________________                                         32      270      21.8       None                                               33.sup.1,2                                                                             370      78         100 ml n-heptane                                                               75 gms HPS/174 gms                                                             styrene                                            34.sup.1                                                                               239      39         10 gms HPS/243 gms                                                             styrene                                            ______________________________________                                          .sup.1 Imbibed mix of rubber and solvent Waring blend mixed 5 minutes.         .sup.2 After polymerization, copolymer dried 22 hours in 155 Deg. C. oven

                                      TABLE IX                                     __________________________________________________________________________     RESULTS OF TESTING                                                             __________________________________________________________________________                                 Notched Izods                                      Chlorobutyl Tensile  Flex   (ft. lbs/in.Notch)                                      Rubber Yield                                                                              % Elong.                                                                            Mod. × 10.sup.-.sup.3                                                           Room                                               Example                                                                             wt. %  (psi)                                                                              fail (psi)  Temp.                                                                              -20 Deg.F.                                     __________________________________________________________________________     32.sup.1                                                                            7.5    6855                                                                               --   386    0.64                                                                               --                                             33   11.2   8900                                                                               8.0  369    1.15                                                                               0.79                                           34   7.3    7610                                                                               6.0  361    0.52                                                                               0.63                                           __________________________________________________________________________      .sup.1 MF.sub.290 (2.16 Kg) = 4.0, Unnotched Izod at -20 Deg. F. = 3.5   

EXAMPLE 35

In this example, crosslinking of the chlorobutyl rubber (HT 1066) was aided during bulk polymerization by the addition of 3 ml of hexamethylene diamine thereto. The reaction was carried out for 6 hours at 60° C. and for 501/2 hrs. thereafter at 90° C. The amount of rubber based on total polymer was 7.4%. The test material showed tensile yield= 5917 psi; percent elongation at failure= 5.2; Flexural modulus× 10⁻ ³ = 317 psi; Notch Izod Room temperature= 0.82,- 20° F.- 0.62.

EXAMPLE 36

In this example, the weaterhing characteristics of a composition according to Ser. No. 497,688 were compared to a commercial high impact graft copolymer. The Ser. No. 497,688 copolymer employed was that prepared according to Example 28. For comparison a commercial sample of polystyrene-polybutadiene graft copolymer* was employed. Both materials were aged in a Xenon weatherometer and the % elongation at rupture determined at various exposure times. The results are set out in the FIGURE. The loss for the CL (Bu)R HIPS (Ex. 28) had only 35% loss in percent elongation at 500 hours whereas the commercial product had totally failed. The samples were pulled at 2 inches per minute. Note also that the PBD-HIPS has deteriorated to the brittle fracture region in less than 200 hours of aging.

A comparison of the included matrix phase polymer contained in the included elastomer phase (chlorobutyl rubber) in the composition of the Ser. No. 497,688 invention by the three principal process embodiments described and shown in the examples, is set forth in TABLE X below.

                  TABLE X                                                          ______________________________________                                                           Wt. % Matrix*                                                       Chlorobutyl                                                                               Phase Polymer                                                       Rubber     in Gel        R. T. Notched                                  Example                                                                               Wt. %      (Elastomer) Phase                                                                            Izod                                           ______________________________________                                          5     7.4        14.6          0.57                                           18     7.4        50.6          1.06                                           24     7.4        60.6          1.31                                           ______________________________________                                          *Weight % of matrix phase in the residue was determined by shaking .about      2 gram samples of the dried beads with 60 ml of a 1:1 methyl ethyl keton       (MEK)-acetone mixture for -> 16 hours. This slurry was then washed with        MEK/acetone into two stainless steel centrifuge tubes and centrifuged ten      minutes at 11,500 RPM. The residue was dried overnight at 70 deg. C. (15       mm Hg) and reweighed.                                                    

Although the actual working examples described above were carried out with chlorobutyl, bromobutyl can be utilized in an identical manner with equivalent or superior results.

It is also to be noted that the crosslinking of the brominated copolymer of the invention is an extremely mild crosslinking, preferably a thermal one carried out in the absence of conventional crosslinking agents with the optional exception of very small quantities of ZnO.

After the mild crosslinking, measurements will not detect significant loss of bromine atoms. 

What is claimed is:
 1. A graft copolymer comprising as the matrix a polymer of styrene or a copolymer of styrene and acrylonitrile and grafted thereto a crosslinked, brominated polymer consisting essentially of isobutylene and 1 to 3 weight percent isoprene and having about one atom of bromine per double bond of uncrosslinked polymer, prepared by the process comprising:crosslinking a brominated polymer consisting essentially of isobutylene and 1 to 3 weight percent isoprene and having about one atom of bromine per double bond of uncrosslinked polymer, imbibing into said crosslinked polymer, styrene or a mixture of styrene and acrylonitrile, containing from about 50 to 80 weight percent styrene, to form a gel, dispersing said gel to a particle size wherein the crosslinked brominated polymer phase in said graft copolymer is less than 10μ diameter, suspending said gel in water, polymerizing said styrene or mixture of styrene and acrylonitrile in the presence of a free radical catalyst, at a temperature in the range of 50° to 150° C., said crosslinked, brominated polymer being present in an amount of from 2 to 30 weight percent based on total styrene or mixture of styrene and acrylonitrile present in said suspension, and recovering a solid graft copolymer of polystyrene or polystyrene-acrylonitrile and included crosslinked, brominated polymer.
 2. The graft copolymer according to claim 1 wherein said graft copolymer is comprised of from 5 to 8 percent of said brominated polymer.
 3. The graft copolymer according to claim 1 wherein said matrix is a polystyrene.
 4. The graft copolymer according to claim 1 wherein said matrix is a copolymer of styrene and acrylonitrile.
 5. A process of preparing a graft copolymer comprising crosslinking a brominated polymer consisting essentially of isobutylene and 1 to 3 weight percent isoprene and having about one atom of bromine per double bond of uncrosslinked polymer,imbibing into said crosslinked polymer, styrene, or a mixture of styrene and acrylonitrile to form a gel, dispersing said gel to a particle size wherein the crosslinked brominated polymer phase in said graft copolymer is less than 10μ diameter, suspending said dispersed gel in water, polymerizing said styrene or mixture of styrene and acrylonitrile at a temperature in the range of 50° to 150° C., said crosslinked, brominated polymer being present in an amount of from 2 to 30 weight percent based on total styrene or mixture of styrene and acrylonitrile present in said suspension, and recovering a solid graft copolymer of polystyrene or polystyrene-acrylonitrile as the matrix and included brominated polymer.
 6. The process according to claim 5 wherein said brominated polymer is dissolved in a mixture comprising 20 to 90 weight percent styrene and 10 to 80 weight percent acrylonitrile.
 7. The process according to claim 5 wherein a mixture of styrene and acrylonitrile containing 50 to 80 weight percent styrene is employed.
 8. The process according to claim 5 wherein an inert diluent of C₅ to C₁₀ saturated hydrocarbon is added to the polymerization.
 9. The process according to claim 5 wherein said brominated polymer is present in the range of 5 to 8 weight percent.
 10. The process according to claim 5 wherein said brominated polymer is crosslinked by heating solid polymer.
 11. The process according to claim 10 wherein styrene is imbibed into said crosslinked brominated polymer.
 12. The process according to claim 10 wherein said heating is in the range of 100° to 200° C.
 13. The process according to claim 11 wherein said suspension polymerization is carried out in the presence of a free radical catalyst.
 14. The process according to claim 13 wherein said catalyst is organic peroxide or organic hydroperoxide. 